The present invention relates to capacitive touch entry structures and more particularly to a structure allowing capacitive touch entry of data while providing a high degree of safety to user personnel.
It is known to provide arrays of at least one conductive touch pad sensor for controlling functions of an apparatus by contact of a portion of the user's personnel, such as a user's fingertip, to a touch contact area. Conventional touch entry systems utilize a matrix of electrodes overlayed by an insulating film, such as a plastic membrane and the like, to allow the electrode to be pressed against contacts by user's finger, while preventing direct contact with the electrode. The insulative plastic membrane allows a low impedance path between a pair of contacts to be made, and also prevents application of touch contact potentials to the user's finger, but is of insufficient insulative thickness to prevent application of higher potentials if such higher potentials appear on the touch contact due to improper generations of the apparatus to be controlled by the touch sensors. This form of touch entry structure exhibits several difficiencies, including: a plastic appearance; a high probability of damage during cleaning (which may allow touch pad potentials to be received by user personnel); and low possibility of integration with display apparatus due to the insufficient clarity of a plastic membrane for allowing the display information to appear in areas directly adjacent to the capacitive touch pad area.
A suggested solution to the problem is to fabricate capacitive touch sensors having touch pad electrodes fabricated upon a glass substrate. The use of a glass substrate generally requires some form of conductive elements upon the front surface of the substrate, which is that surface directly contacted by the user's finger. Thus, not only is the user receiving some portion of the voltage potential utilized to operate the sensor (which is undesirable from a safety viewpoint) but this form of capacitive touch pad also requires the extremely expensive processing step associated with depositing a front substrate conductor and is also incompatible with the processes utilized for tempering the glass substrate for safety reasons. Additionally, the front electrode must be of a transparent conductive material and tends to show fingerprints more readily than a glass substrate having no front substrate conductor; the presence of a front substrate conductive film allows that film to be interrupted, as by the presence of scratches and the like, whereby the capacitive touch sensor utilizing that electrode will fail.
Accordingly, it is desirable to provide a capacitive touch entry panel structure having capacitive touch entry sensors so positioned as to provide a high degree of user safety and sensor reliability, with low manufacturing costs therefor.